Find the Directional derivative of the function u

asi123
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Homework Statement



Hey.
I need to find the Directional derivative of the function u, in the direction l, in the point m (all in the pic).
I'm not sure I did it right, can you please give me the ok?


Homework Equations





The Attempt at a Solution


 

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Up to DLu= (1/3)(2x- z)+ (2/3)cos y+ (2/3)x, everything looks good. Then you evaluate that at (1,\pi/2, -3) and get 7/10? That's not what I get.
 
HallsofIvy said:
Up to DLu= (1/3)(2x- z)+ (2/3)cos y+ (2/3)x, everything looks good. Then you evaluate that at (1,\pi/2, -3) and get 7/10? That's not what I get.

Oops, got 7/3?
 
Yes, that is correct. I wondered where that "10" came from!
 
HallsofIvy said:
Yes, that is correct. I wondered where that "10" came from!

Broken calculator...:smile:

No, just kidding, it was early in the morning.
 

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